A girl accused of killing a mother and her daughter told police she and her co-accused had tried twice previously to kill them, a court heard.
Elizabeth Edwards, 49, and her 13-year-old daughter Katie were found dead in Spalding in April.
The 15-year-old denies murder, but has admitted manslaughter on the grounds of diminished responsibility, at Nottingham Crown Court.
A boy, also 15, has already pleaded guilty to murder.
Neither teenager can be named because of their ages.
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On the second day of the trial transcripts of the girl’s police interviews were read.
She told officers she and her co-accused had planned the killings, which had started off as a joke, in the days before their deaths on the evening of 13 April.
She said she had “felt like murdering for quite a while”.
“A gun would have been easier but we don’t have any really in this country,” she said.
“The knife was a better solution.”
She also said they had attempted to carry out the killings on two other occasions.
When officers asked her how her boyfriend, who was 14 at the time, had seemed after the killings, she said: “He seemed fine. I don’t know how he’s feeling now but at that moment in time he seemed fine.”
Asked how she felt, she said: “I was ok with it. Just the fact that it happened so quickly gave me peace of mind.”
She told police her co-accused had stabbed Ms Edwards in the neck and then smothered her.
“He walked into the room and he kind of climbed onto the bed,” she said.
“He was on top of her [Ms Edwards], he had a pillow over her face. Then after about 10 minutes of him putting his weight on her, she was dead.
“There was a little bit of blood spattered on the wall and there was a lot of blood on the bed.”
She added she did not see Katie’s death but heard her mumble something as she was killed.
The teenager told detectives the plan had been for her and the boy to take their own lives after the killings and had left a note requesting her ashes be scattered at a special place.
The trial continues.
Read more: http://www.bbc.co.uk/news/uk-england-lincolnshire-37621177